You prolly chewed up the plastic gear that drives the speedo sensor. Mine is mounted on the transmission tailshaft, I believe yours is mounted on the xfer case. Remove it and count the teeth. Not really that expensive. Note what position the sensor is in before you remove it. If you install the new one and the sensor is not rotated correctly you will just eat it up too. If the gear is good then you need a new sensor. They changed plug styles so it will involve some wiring work. While you have it apart also look at how long the square shaft that goes into the gear is. Mine broke and only left about a quarter inch of square shaft. I became an expert at R&R until I got the new sensor and saw how long a good shaft is.